1. Field of the Invention
This invention relates generally to power supply systems for supplying power to plasma processing systems, and more particularly to power supply systems with arc detection and arc reduction capabilities for eliminating arcs generated in a plasma processing chamber.
2. Brief Description of the Preferred Embodiment
In plasma processing systems a DC power supply creates an electric potential between a cathode and anode to create plasma. In the deposition mode, the plasma then acts upon a material target to create a thin film on some substrate. One of the challenges in many such applications is that electrical discharges or arcs can occur. As one example, a reactive coating process is particularly challenging because it often involves forming insulating regions on the material target and bombarding them with ions. This leads to charging of the insulating regions which can cause electrical breakdown of the insulator. As a result, the electrical environment during plasma processing can be particularly conducive to arc discharges. These arc discharges are undesirable not only because they represent potential non-uniformities in the coating process, but also because they can lead to the creation of particulates which can in turn create defects in sensitive items such as computer disks and integrated circuits processing. One solution has been the utilization of frequency-oriented components to discharge a capacitor through an inductor in such a way as to reverse the current to negate or quench the arc.
Most arc reduction circuits utilize a voltage detector to detect arcs. In these circuits a logic circuit and a low voltage power supply has to be added to the power supply or other arc reduction equipment to power the arc reduction features. Also, the circuit needs to be disabled at startup of the power supply to avoid false arc trips. This is especially critical, if the power supply has to start into a low impedance load, like into a chamber with another plasma discharge already existent. Additionally, the arc detection to a low voltage level can cause a substantial delay to the arc detection or even ignore higher voltage arcs often observed in plasma processes. Lastly, the arc detection and reduction should be simple reliable and control the switches to remove the energy from the plasma discharge quickly. The speed of the reaction to turn off the arc is very important. If the arc is turned off is too fast, the arc density over time can increase and a long-term stable process may be difficult to obtain. If the arc is turned off too slow, the energy fed into the arc can be too big and can reduce the quality of the film or the substrate.
It would be desirable if there were provided an arc detection and arc reduction circuit that was simple and reliable without the need for complicated detection circuits and auxiliary power supplies. It would also be desirable if the circuit did not utilize high voltage bridging components.